A typical cryopump includes a cryogenic refrigerator that produces refrigeration at two temperature stages. The first stage of the cryogenic refrigerator typically operates in the range of 50 to 75K and is used to cool the outer cryopanel and the louvers across the inlet of the pump. The second stage of the cryogenic refrigerator is the coldest stage and typically operates in the range of 10 to 20K. The second stage is used to cool the inner cryopanel.
In a typical cryopump, water vapor freezes out on the louvers. Nitrogen, oxygen and argon freeze out on the outer surface of an inverted U-shape substrate. Hydrogen, helium, and neon are adsorbed on a layer of charcoal attached to the inner surface of the substrate. Charcoal or some other cryosorbing material is provided to absorb the hydrogen, helium and neon since their equilibrium vapor pressures are too high at 20K to be cryo-condensed on the bare substrate. Activated charcoal is the preferred cryosorbing material because it has a large surface area and gases desorb from charcoal quite readily at room temperature during regeneration. The cryosorbing material is provided on the inner surface of the U-shaped substrate so as to be protected from the air gases which otherwise would coat the surface and fill the pores thereby rendering them inaffective for pumping.
The present invention is directed to a solution of the problem of how to increase the efficiency of cryosorbing molecules of hydrogen, helium and neon.